Assessment of appropriate l-cysteine concentration for boar semen cryopreservation by using flow cytometry

The present study aims to investigate a suitable L-cysteine level to be added the lactose-egg yolk (LEY) extender to improve the quality of boar semen after freezing-thawing using Annexin-V and propidium iodide (PI) assay detected with flow cytometer. Ejaculates from twelve boars were processed in the LEY extender and added with 0, 5, 10 and 15 mM of L-cysteine. Semen suspensions were cryopreserved with a controlled-rate freezer and thawed for examination. The surface of sperm plasma membrane was explored by scanning electron microscopy (SEM) while sperm membrane integrity was performed by Annexin-V/PI assay. Of all treatments, the damaged spermatozoa in various patterns were observed whereas the intact spermatozoa were still found by SEM. The viable and non-apoptotic (AN-/PI-) sperms were higher (p< 0.05) in the levels of 5 and 10 mM. These results indicated that the damaged spermatozoa were found after freezing/thawing and the L-cysteine at concentrations of 5 to 10 mM added to LEY extender was the optimal dose against oxidative stress and acquisition for improving cryopreserved boar sperm quality.